1. Field of the Invention
The present invention relates to spark ignition engines comprising a single chamber type combustion chamber.
2. Background Art
Conventionally, in order to achieve the stable ignition performance even with the leaner air-fuel mixture, the spark ignition engine comprising the single chamber type combustion chamber comprises an ignition plug, which is provided in an auxiliary chamber without fuel supply (e.g. see JP-A-4-287826). In the spark ignition engine like this, as shown in FIGS. 15 and 16, a combustion chamber 25 is formed between a cylinder head 21 and the top of a piston 23 installed in a cylinder 22, and an ignition plug 27 is provided in the cylinder head 21 in such a way that ignition electrodes 27a are disposed over the combustion chamber 25. A cap 28 having a plurality of nozzle holes 28a is provided at the tip of the ignition plug 27 so as to cover the ignition electrodes 27a, and an auxiliary chamber 30 is thus formed in the cap 28, communicated with the combustion chamber 25 through the plurality of nozzle holes 28a. Therefore, when the air-fuel mixture flowed into the auxiliary chamber 30 from the cylinder 22 is spark-ignited with the ignition electrodes 27a of the ignition plug 27, the flame blown off out of the plurality of nozzle holes 28a becomes a flame jet. The flame jet makes the turbulence and is transmitted into the combustion chamber 25. As a result, the air-fuel mixture in the combustion chamber 25 is fully combusted. Hence, the turbulence generated by the flame jet makes the rapid combustion possible.